The present invention relates to fluidic, electrical, electronic, and optical flex circuits and connections thereto.
Flex circuits, also known as flexible circuits, flexible printed circuit boards, and flexible printed wiring, are circuits made in or on flexible substrates. While the substrates are usually substantially planar, they may be bent and folded in order to accommodate themselves to three-dimensional shape requirements.
Flex circuits are typically made of a flexible insulating material for example a polyimide such as KAPTON, a registered trademark of E.I. du Pont de Nemours and Co., Inc., although many other materials including paper, polyamide, polyester terephthalate (PET), random-fiber aramid (ex. NOMEX, a registered trademark of E.I. du Pont de Nemours and Co., Inc.), and polyvinyl chloride (PVC) may be used. Electrical leads and electrical devices such as microchips can be embedded within or upon the flex circuit. Fluid wells and trenches can be recessed within the surface of the flex circuit, and fluid capillary channels can be embedded within the flex circuit. Optical devices, for example, fiber optic elements, optical gratings, optical sources, and optical receivers can be embedded within or upon the flex circuit. A flex circuit having only electrical leads is often called an electrical flex circuit, while a flex circuit having fluid wells, trenches, or capillary channels is often called a fluid flex circuit or a microfluidic circuit. A flex circuit-with optical elements can be referred to as an optical flex circuit or a flexible optical circuit; see, for example, U.S. Pat. Nos. 5,902,435; 6,005,991; 6,069,991; 6,088,498; and 6,222,976. Fluid flex circuits and microfluidic circuits can include electrical elements; see, for example, U.S. Pat. Nos. 5,645,702; 5,658,413; 5,804,022; 5,882,571; and 6,093,362. The advantageous three-dimensional nature of flex circuitry is well known. See, for example, U.S. Pat. No. 4,928,206.
Often it is difficult, costly, or both, to combine more than one of electrical, fluidic, and optical elements in the same flex circuit. It is often more cost effective to build electrical, fluidic, and optical components as separate subsystems and then connect the subsystems together. The final device may then be a composite of several different electrical, fluidic, and optical subsystems and may even incorporate other subsystems such as micro-electro-mechanical systems (MEMS) or micro-optical-electro-mechanical systems (MOEMS). Often, subsystems are designed to join with other subsystems and to interact directly with the other subsystems. However, in some cases the subsystems must interact through electrical, fluidic, or optical leads. These leads may join to the subsystems at bonding points. The bonding points are generally physically weaker than the leads and the subsystems to which they join. If the leads are moved or flexed in relation to their associated bonding points, then the bonding points may be loaded in tension and subjected to bending and torsional forces. The moving and flexing can cause failure at the bonding points.
Connecting a flex circuit type subsystem to a second subsystem, such as another flex circuit, a rigid printed circuit board, or a microchip, often requires approaching a planar surface of the second subsystem from out of the plane of the second subsystem. This transition in directions can result in strain on the bonding points between the first and second subsystem.
Prior art devices have focused on strengthening the bond at the bonding points, but space limitations and material constraints limit the ultimate strength of the bond. Therefore, there is a need for a manner of attaching leads in a flex circuit device that minimizes the loading, and thus the vulnerability of the bonding points.
There also exists a need for a cost-effective method of attaching a flex circuit to a system or subsystem in a manner which transfers the flex circuit from an attachment surface of the system or subsystem, through the plane of the surface, to an opposing surface of the system or subsystem.
The invention generally provides a system of securing a flex circuit relative to a bonding region in such a manner as to limit the loading at the bonding region and minimize the likelihood of a failure of the juncture. The invention also provides a cost-effective method of transferring a flex circuit from an attachment surface of a system through the plane of the surface to an opposing surface of the system.
The invention encompasses a flexible circuit device having a support member for supporting a lead bonding region. The support member has at least two apertures therein. A flexible lead is connected to the lead bonding region and woven through the apertures such that the flexible lead is retained in the support member in relation to the lead bonding region.
Mechanical or adhesive means may further be used to secure the flexible lead to the support member, wherein the mechanical or adhesive means have a greater rupture strength than the strength of the bond between the flexible lead and the second lead bonding region.
An advantage of the invention is that the flexible lead is secured in a position so as not to impart tensile and bending loads on the bonding point, thus minimizing the possibility of failure of the bond.
Another advantage of the invention is that if the support member is flexible, tension in the support member increases the frictional engagement of the flexible lead.
Another advantage of the invention is that the flexible lead can pass through the plane of the support member.
The above advantages and additional advantages will become apparent from the following detailed description when taken in conjunction with the accompanying drawings.